MILK-SUGAR. 225 



Formalin cannot be estimated with any degree of exactitude, 

 as it gradually enters into combination with the proteins present, 

 and only the residue of uncombined formaldehyde, which gives 

 no clue to the original amount, can be determined. 



If adulteration is suspected, it may be of interest to examine 

 microscopically the residue left after removal of the fat ; 

 adulterants, such as starch, mineral matters, etc., which it is 

 alleged have been used, would be thus detected. This form of 

 adulteration is of extreme rarity, but starch is sometimes added 

 to ear-mark margarine. 



Examination of Commercial Milk-sugar. Add 6 or 7 

 grammes of the finely-powdered sugar to about 50 c.c. of dis- 

 tilled water ; stir vigorously with a thermometer for ten seconds 

 and allow the solution to settle for twenty seconds ; read the 

 fall in temperature on dissolution and filter the solution rapidly. 

 When sufficient clear filtrate is obtained, fill a 200 mm. polari- 

 scope tube, and polarise as soon as possible. Take polarimetric 

 readings every minute till the specific rotatory power begins to 

 diminish. If the temperature at which the solution is polarised 

 is kept at 15 C., or below, there is no difficulty in obtaining 

 several readings which are nearly constant, and the mean of 

 these are taken as the initial rotation. Allow the tube to stand 

 for twenty-four hours, and polarise again at the same tempera- 

 ture ; this is the normal rotation. The initial rotation divided 

 by the normal rotation will give the " birotation ratio." The 

 amount of milk-sugar in 100 c.c. of this solution is estimated, 

 either by drying 5 c.c. at 100 C., when a residue of anhydrous 

 sugar will be left, or by deducing it from the normal rotation. 

 This is done by dividing the reading in angular degrees by 1-106. 

 The two figures should agree closely. 



About 10 grammes of sugar are weighed out into a 100 c.c. 

 flask and boiled with about 80 c.c. of water for a few minutes. 

 The solution is cooled to 20, made up to 100 c.c., and polarised 

 in a 200 mm. tube. The reading in angular degrees multiplied 

 by 100 and divided by the weight of sugar taken multiplied by 

 1 -05 will give the percentage of milk-sugar in the sample. 



To a solution in water (10 per cent.) a little mercuric nitrate 

 is added ; the solution should not show more than the faintest 

 turbidity. 



Five grammes are weighed out in a platinum basin, ignited 

 over a moderate flame and the ash weighed. 



Ten grammes are dissolved in 100 c.c. of milk ; this is brought 

 to the boil ; the milk should not be curdled. The acidity 

 should be estimated by titrating 5 grammes dissolved in water 



N 

 with alkali and calculated as lactic acid. 



15 



